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EMBO J. 1993 Jan;12(1):303-6.

Millisecond studies of secretion in single rat pituitary cells stimulated by flash photolysis of caged Ca2+.

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  • 1Department of Physiology and Biophysics, University of Washington, Seattle 98195.


To study the final steps in the secretory pathway of rat pituitary melanotrophs, we have monitored changes in cell surface area due to exocytosis after flash photolysis of caged Ca2+. A step increase in cytosolic [Ca2+] to 45-125 microM triggers three phases of exocytic secretion. A small cohort of a few hundred vesicles is exocytosed in 40 ms in a secretory burst with a peak rate of 17,000 vesicles/s. Next, 2700 more vesicles are released in a slower phase that is complete within 400-1000 ms. Finally, vesicles continue to be released slowly (500 vesicles/s) for > 8s. The approach described provides a way to identify and monitor the final steps in the secretory pathway at millisecond resolution. That a small portion of secretory vesicles can be released much faster than all others suggests that these vesicles are functionally equivalent to those at the presynaptic active zone of a neuron. Their release would be fast enough to be temporally correlated with single action potentials.

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